Photosensitive members such as electrophotographic or photoconductive members, including photoreceptors or photoconductors, typically include a photoconductive layer formed on, for example, an electrically conductive substrate or formed on layers between the substrate and photoconductive layer. The photoconductive layer is an insulator in the dark so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated. In this manner, an image, for example a latent image, can be formed on the photoreceptor, developed using a developer material such as toner, transferred to an image receiving substrate such as paper, and fused thereto to form a copy or print.
As noted in several of the patents discussed in the above discussion, a significant property in photoreceptors is wear resistance, and improved wear resistance is always being sought. For example, advanced imaging systems are based on the use of small diameter photoreceptor drums, and the use of small diameter drums places a premium on photoreceptor life. Small diameter drum photoreceptors are particularly susceptible to wear because about 3 to 10 revolutions of the drum may be required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can thus require about 1 million cycles or more from the photoreceptor drum to obtain 100,000 prints, a desirable print job goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the microcorona generated by the BCR during charging damages the photoreceptor, resulting in rapid wear of the imaging surface, for example, the exposed surface of the charge transport layer. More specifically, wear rates can be as high as about 10 microns per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems and belt systems. One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, for example on the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, avoidance of perturbation of underlying layers during coating.
Despite the various approaches that have been taken for forming overcoating layers, there remains a need for improved overcoat layer design, to provide increased wear resistance as well as resistance to moisture such as humidity and the like. Achieving these properties can increase the useful life of the photoreceptor and/or increase the range of environments and printing apparatus in which the photoreceptor can be used.